21BB Base Settings

This walkthough explains how to return to base settings (factory
settings) on your 21BB engine.

The HPI 21BB engine has got a three needle carburetor with a
high speed, a mid-range, and a low speed needle. Therefore bringing
the low speed needle to it's base setting is slightly different
from a two needle carburetor. In this walk through we will show you
the differences between adjusting the 21BB engine and adjusting the
S-25 as shown in great detail on the HPI RC cars DVD. For your 21BB
engine we recommend watching the getting started S-25 video on the
HPI RC cars DVD and reading this walkthrough in addition. There are
also two video clips at the end of this page showing how to adjust
the 21BB engine.

We start with the high speed needle.

Turn the needle clockwise until it is closed. This shuts off all
fuel supply, then open three and a half turns anticlockwise, this
is the base setting for the high speed needle. In most cases the
high end needle is the only one which needs adjustment. So if you
have problems always try resetting this high end needle to the base
setting first.

Now turn the midrange needle clockwise until it is
closed.

From closed, open three and a quarter turns, this is the base
setting for the mid-range needle.

To return the low speed needle to its base settings you have to
hold the mid-range needle with a screw driver to prevent it from
being turned.

Then cerfully turn the low speed needle clockwise until you can
feel it is turning the midrange needle. Be carefull not to loose
the base settings of the midrange needle. Then, still holding the
mid-range needle, open the low-speed needle 3 and a half turns.
This is the base setting of the low speed needle. You will use this
base setting for breaking in the engine and as a starting point for
the tuning process or fault finding.